1. Field of the Invention
The present invention relates to ink jet printing apparatus and more particularly to constructions that provide improved diagnostic capabilities, as well as improved start-up and storage capabilities for such apparatus.
2. Description of the Prior Art
The term "continuous" has been used in the field of ink jet printer apparatus to characterize the types of ink jet printers that utilize continuous streams of ink droplets, e.g. in distinction to the "drop on demand" types. Continuous ink jet printers can be of the binary type (having "catch" and "print" trajectories for droplets of the continuous streams) and of the multi-deflection type (having a plurality of print trajectories for droplets of the continuous streams). Binary type apparatus most often employs a plurality of droplet streams while multi-deflection apparatus most often employs a single droplet stream.
Binary, continuous ink jet printing apparatus have an ink cavity to which ink is supplied under pressure so as to issue in streams from an orifice plate that is in liquid communication with the cavity. Periodic perturbations are imposed on the liquid stream (e.g. vibrations by an electromechanical transducer) to cause the streams to break up into uniformly sized and shaped droplets. Charge electrodes located proximate the stream break-off point are activated to impart electrical charge in accord with a print information signal and nonprinting droplets are deflected into a catcher assembly.
It is important in such apparatus that the break-off point of the ink filaments occurs opposite their respective charge electrodes and that the phase of the filament break-off (i.e. the droplet formation) be properly synchronized with the phase of the information signal that controls activation or nonactivation of the electrodes. A variety of useful approaches for diagnosing proper break-off and synchronization have been developed in the past. U.S. Pat. No. 3,761,941 discloses one system wherein an electrometer, connected to the droplet catcher, is utilized to indicate deviations in phase between droplet break-off and the charging signals. This approach requires that all drops always be receiving a sufficient charge to impart a catching deflection, which can be disadvantageous in implementing some desirable diagnostic/correction approaches.
U.S. application Ser. No. 06/722,551 filed Apr. 12, 1985, and entitled "Ink Jet Printing Apparatus Having a Wet Storage System", discloses a home station, adjacent the operative printing positions of a print head assembly, which is useful for storing that assembly in a wet condition and in collecting ink during start-up operations, for return to the main ink supply.
It has been discovered that by incorporating certain detection and ink handling structures into a home station, such as disclosed in my above-mentioned application, improved diagnostic capabilities can be provided for ink jet printing apparatus.